Hologram reproduction process and volume hologram

ABSTRACT

The invention relates to a method for replicating a volume hologram having an image of a scattering object recorded therein according to a hologram replicating technique, wherein the diffraction 13 of an unnecessary order of light due to zero-order light, etc. arising from regular reflection and a visual range capable of viewing a recorded image is limited to a desired range α, so that the image can be displayed more brightly than would be possible with the original hologram plate, and a volume hologram as well. When replicating a volume hologram 4&#39; having an image O&#39; of a scattering body recorded therein, replicating illumination light is incident on the volume hologram 4&#39; at an angle of incidence I 1  at which a group of fringes can be replicated and recorded, said group of fringes being such that, in the vicinity of an apex defined by a supposed slant angle S g  at which a replicated hologram 4&#39; can be viewed at a supposed viewing center angle φ within a range α upon illumination with illumination light 7 at a supposed illumination angle θ, a recording degree of said group of fringes becomes weaker at a position farther away from said slant angle S g .

BACKGROUND OF THE INVENTION

The present invention relates generally to a hologram-replicating (orcopying) method and a volume hologram, and more particularly to a methodfor replicating (or copying) a volume hologram having an image of ascattering object recorded therein by a hologram replicating technique,wherein the diffraction of an unnecessary order of light (zero-orderlight) is limited and a visual range (angle-of-view range) where therecorded image can be viewed is limited to a desired range, so that animage brighter than that in the original hologram plate can bedisplayed, and a volume hologram.

So far, it has been well known in the art that scattering light comingfrom a scattering object and reference light interfere in a volumehologram photographic material to record a volume hologramreconstructible in white illumination light. Also well known in the artis a hologram replicating technique wherein a reflection or transmissiontype volume hologram is provided thereon with another volume hologramphotographic material, and laser light is allowed to be incident on saidanother photographic material or the original hologram plate so thatsaid incident light and light diffracted by the volume hologram caninterfere in said another photographic material, whereby the originalvolume hologram can be copied to obtain the same hologram.

When copying a volume hologram with a scattering object recorded thereinby the hologram replicating technique, however, the angle of incidenceof the copying laser light has been selected from those in the vicinityof the angle of incidence of the reference light used for recording theoriginal hologram plate or otherwise no special care has been takenthereof at all. For this reason some problems have arisen. For instance,unnecessary interference fringes coming from light (zero-order light)produced by the regular reflection of light from the scattering objectremain recorded in the copied hologram, or unnecessary diffracted lightarises from unnecessary interference fringes because the visual rangewhere the recorded image can be viewed is as wide as that of theoriginal hologram plate. Consequently, no satisfactorily bright displaycan be obtained.

SUMMARY OF THE INVENTION

In view of such problems with the prior art, an object of the presentinvention is to provide a method for replicating a volume hologram withan image of a scattering object recorded therein by the hologramreplicating technique, wherein the diffraction of an unnecessary orderof light due to zero-order light, etc. arising from regular reflectionis limited and a visual range where the recorded image can be viewed islimited to a desired range, thereby obtaining a hologram capable ofpresenting an image display brighter than would be possible with theoriginal hologram plate, and a volume hologram.

Another object of the present invention is to provide a hologram displaypiece that is one volume hologram which has an image of a scatteringbody recorded therein, and to which the aforesaid hologram replicatingmethod is applied, and a process for fabricating the same.

Yet another object of the present invention is to provide a hologramliquid crystal display timepiece comprising a reflection type diffusehologram layer that is a volume hologram which has an image of ascattering body recorded therein, and to which the aforesaid hologramreplicating method is applied.

According to one aspect of the present invention, there is provided amethod for replicating an original volume hologram plate having an imageof a scattering body recorded therein according to a hologramreplicating technique, characterized in that replicating illuminationlight is incident on said original volume hologram plate at an angle ofincidence I₁ at which a group of fringes can be replicated and recorded,said group of fringes being such that, in the vicinity of an apexdefined by a supposed slant angle S_(g) at which a replicated hologramcan be viewed at a supposed viewing center angle φ upon illuminated at asupposed illumination angle θ, the recording degree of said group offringes becomes weaker at a position farther away from the slant angleS_(g).

Preferably in this case, the angle of incidence I₁ should satisfy:##EQU1## wherein: I₀ is an angle of incidence of reference light torecord said original volume hologram plate,

λ₀ is an wavelength at which the original volume hologram plate isrecorded,

ν₀ is a degree of shrinkage of a photographic material with the originalvolume hologram plate recorded therein,

τ₀ is a slant angle change of fringes recorded in the original volumehologram plate,

λ₁ is a wavelength to replicate the original volume hologram plate,

τ₁ is a slant angle change of replicated fringes,

n₀ is an external refractive index of the photographic material, and

n₁ is an internal refractive index of the photographic material.

According to another aspect of the present invention, there is provideda method for replicating an original volume hologram plate with a firstvolume hologram having an image of a first scattering body recordedtherein and a second volume hologram having an image of a secondscattering body recorded therein, said holograms superposed on eachother, in a single volume hologram photographic material according toclaim 1 or 2, characterized in that replicating illumination light isincident on the original volume hologram plate at an angle of incidenceI₁ at which a first group of fringes, a second group of fringes, and atleast one additional similar group of fringe can be replicated andrecorded, said first group of fringes being such that, in the vicinityof an apex defined by a first supposed slant angle S_(g1) at which areplicated hologram can be viewed at a first supposed viewing centerangle φ₁ upon illuminated at a supposed illumination angle θ withrespect to the hologram image of the first scattering object, arecording degree of said first group of fringes becomes weaker at aposition farther away from the slant angle S_(g1), and said second groupof fringes being such that, in the vicinity of an apex defined by asecond supposed slant angle S_(g2) at which the replicated hologram canbe viewed at a second supposed viewing center angle φ₂ different fromthe first supposed viewing center angle φ₁ upon illuminated at thesupposed illumination angle θ with respect to the hologram image of thesecond scattering object, a recording degree of said second group offringes becomes weaker at a position farther away from the slant angleS_(g2).

According to yet another aspect of the present invention, there isprovided a method for replicating an original volume hologram plate witha first volume hologram having an image of a first scattering bodyrecorded therein at a first wavelength and a second volume hologramhaving an image of a second scattering body recorded therein at a secondwavelength, said holograms superposed on each other, in a single volumehologram photographic material according to claim 1 or 2, characterizedin that replicating illumination light is incident on the originalvolume hologram plate at an angle of incidence I₁ at which a first groupof fringes, a second group of fringes, and at least one similar group offringes can be replicated and recorded, said first group of fringesbeing such that, in the vicinity of an apex defined by a first supposedslant angle S_(g) at which a replicated hologram can be viewed at asupposed viewing center angle φ upon illuminated at a supposedillumination angle θ with respect to the hologram image of the firstscattering body using third illumination light having a constantwavelength ratio relation to the first wavelength, a recording degree ofsaid first group of fringes becomes weaker at a position farther awayfrom the slant angle S_(g), and said second group of fringes being suchthat, in the vicinity of an apex defined by the same supposed slantangle S_(g) at which the replicated hologram can be viewed at the samesecond supposed viewing center angle φ upon illuminated at a supposedillumination angle θ with respect to the hologram image of the secondscattering object using fourth illumination light having again aconstant wavelength ratio relation to the second wavelength, a recordingdegree of said second group of fringes becomes weaker at a positionfarther away from the same slant angle S_(g).

The present invention also includes a volume hologram fabricated by anyone of the aforesaid fabrication methods.

According to a further aspect of the present invention there is provideda volume hologram having an image of a scattering body recorded therein,characterized in that recorded therein is only a group of fringes lyingat slant angles in a given width ΔS with respect to a slant angle S_(g)at which a fringe can be viewed at a given viewing center angle φ uponilluminated at a given illumination angle θ.

According to a further aspect of the present invention, there isprovided a volume hologram having an image of a scattering body recordedtherein, characterized in that recorded therein are a first group offringes lying at slant angles in a given width ΔS₁ with respect to aslant angle S_(g1) at which a fringe can be viewed at a given viewingcenter angle φ₁ upon illuminated at a given angle θ, a second group offringes lying at slant angles in a given width ΔS₂ with respect toanother slant angle S_(g2) at which a fringe can be viewed at anotherviewing center angle φ₂ upon illuminated at said given illuminationangle θ, and at least one additional similar group of fringes.

According to a further aspect of the present invention, there isprovided a volume hologram having an image of a scattering body recordedtherein, characterized in that recorded therein a first group of fringeslying at slant angles in a given width ΔS₁ with respect to a slant angleS_(g) at which a fringe can be viewed at a given viewing center angle φupon illuminated with illumination light of a first wavelength at agiven angle θ, a second group of fringes lying at slant angles in agiven width ΔS₂ with respect to the slant angle S_(g) at which a fringecan be viewed at the same viewing center angle φ upon illuminated withillumination light of a second wavelength at the same given illuminationangle θ, and at least one additional similar group of fringes.

Preferably in these aspects, the hologram image should be recorded insuch a manner that it is reconstructed in the vicinity of a hologramsurface.

The hologram replicating method of the present invention provides areplicated hologram which can display a hologram image more brighterthan would be possible with the original hologram plate because thediffraction of an unnecessary order of light due to zero-order light,etc., arising from regular reflection is limited and the visual rangecapable of viewing a recorded image is limited to a desired range. Thisfeature of the present invention is due to the fact that replicatingillumination light is incident on the original hologram plate at anangle of incidence I₁ at which a group of fringes can be replicated andrecorded, said group of fringes being such that, in the vicinity of anapex defined by a supposed slant angle S_(g) at which the replicatedhologram can be viewed at a supposed viewing center angle φ uponilluminated at a supposed illumination angle θ, the recording degree ofsaid group of fringes becomes weaker at a position farther away fromsaid slant angle S_(g).

According to a further aspect of the present invention, there isprovided a combined reflection and volume phase type of hologram displaypiece, characterized in that a virtual opening and a fine pattern arerecorded with a spatial distance therebetween in a reconstructiblemanner so that the fine pattern located behind the virtual opening canbe seen through the virtual opening.

According to a further aspect of the present invention, there isprovided a combined reflection and volume phase type of hologram displaypiece, characterized in that a fine pattern provides a non-diffractionarea within a hologram surface, and a virtual opening is recorded at aspatial distance from the hologram surface in a reconstructible mannerso that the non-diffraction area located behind the virtual opening canbe visually discriminated through the virtual opening from a diffractionarea.

Preferably in these aspects, a position where the virtual opening isreconstructed should be a surface in the vicinity of the hologramsurface.

According to a further aspect of the present invention, there isprovided a method for fabricating a hologram display piece,characterized by comprising steps of:

irradiating and deactivating an area of a first volume phase typehologram photographic material layer with light while leaving intactother area of the photographic material layer corresponding to a virtualopening pattern,

allowing light to be incidence on the partially deactivated area of thefirst volume phase type hologram photographic material layer so that theincident light, and scattering light that is transmitted through thefirst volume phase type hologram photographic material layer andreflected from a reflecting scatter surface located on an opposite sideof the first volume phase type hologram photographic material layerinterfere in the intact pattern area of the first volume phase typehologram photographic material layer to create an original reflectionhologram plate,

irradiating and deactivating a fine pattern area of a second volumephase hologram photographic material layer corresponding to a finepattern with light, and

allowing light to be incident on the partially deactivated second volumephase type hologram photographic material layer that is located on theoriginal reflection hologram plate at a distance therefrom, so that theincident light, and light that is transmitted through the second volumephase type hologram photographic material layer and reflected anddiffracted by the original reflection hologram plate interfere in anon-deactivated area of the second volume phase type hologramphotographic material layer to create a reflection hologram.

According to a further aspect of the present invention, there isprovided a method for fabricating a hologram display piece,characterized by comprising steps of:

irradiating and deactivating an area of a first volume phase typehologram photographic material layer with light while leaving intactother area of the photographic material layer corresponding to a virtualopening pattern,

allowing light to be incidence on the partially deactivated area of thefirst volume phase type hologram photographic material layer so that theincident light, and scattering light that is transmitted through thefirst volume phase type hologram photographic material layer andreflected from a reflecting scatter surface provided on an incidenceside with an absorptive pattern corresponding to a fine patterninterfere in a non-deactivated pattern area of the first volume phasetype hologram photographic material layer to create an originalreflection hologram plate, and

allowing light to be incident on a second volume phase type hologramphotographic material layer that is located on the original reflectionhologram plate at a distance therefrom, so that the incident light, andlight that is transmitted through the second volume phase type hologramphotographic material layer and reflected and diffracted by the originalreflection hologram plate located on an opposite side thereof interferein a non-deactivated area of the second volume phase type hologramphotographic material layer to create a reflection hologram.

It is understood that the present invention also includes hologramdisplay pieces fabricated by these fabrication methods.

The hologram display piece of the present invention, and the method forfabricating the same enables a fine pattern located behind a smallvirtual opening like a keyhole to be seen through the virtual opening.Between the virtual opening and the fine pattern there is so a certaindistance that the fine pattern seen through and behind the virtualopening can move and change upon the movement of the observer's visualpoint. Such action makes it possible to obtain a display piece that isdifficult to forge and can easily pass judgment on whether an articlehaving it attached thereto is true or not.

According to a further aspect of the present invention, there isprovided a hologram liquid crystal display timepiece, characterized inthat a reflection type diffuse hologram layer is located on a back sideof a liquid crystal panel, said reflection type diffuse hologram layerhas a lateral offset function so as to be free of regularly reflectedlight.

According to a further aspect of the present invention, there isprovided a hologram liquid crystal display timepiece, characterized inthat a transmission type diffuse hologram layer is located on a frontsurface of a liquid crystal panel and a reflecting layer is located on aback surface thereof, said transmission type diffuse hologram layer hasa lateral offset function so as to be free of regularly reflected light.

According to the hologram liquid crystal display timepiece of thepresent invention, visibility can be improved because the reflectiontype diffuse hologram is disposed on the back surface of the liquidcrystal panel or the transmission type diffuse hologram is disposed onthe front surface of the liquid crystal panel, and each hologram has alateral offset function so as to be free of light produced by theregular reflection of ambient light. A variety of aesthetic effects canalso be achieved by recording logotype marks or various patterns in theholograms.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrative of how to record an original volumehologram.

FIG. 2 is a schematic illustrative of how to replicate or copy ahologram from the original volume hologram according to the presentinvention.

FIG. 3 is a schematic illustrative of an illumination angle and acentral viewing angle assumed for a replicated volume hologram.

FIGS. 4(a) and 4(b) are comparative graphs showing the fringe slantangle vs. fringe pitch relation concerning two specific angles ofincidence of replicating illumination light.

FIG. 5 is a graph with the fringe slant angle vs. fringe pitch relationexpressed by exemplary numerical values.

FIGS. 6(a) and 6(b) are schematics illustrative of the qualitativecomparison between a conventional volume hologram and a volume hologramobtained by the hologram replicating method of the present invention.

FIG. 7 is a schematic illustrative of one exemplary application of thevolume hologram copied by the hologram replicating method of the presentinvention.

FIG. 8 is a schematic illustrative of another exemplary application ofthe hologram.

FIGS. 9(a)-9(c) are schematics illustrative of yet another exemplaryapplication of the hologram.

FIGS. 10(a)-10(c) are is schematics illustrative of a part of thehologram display fabricating method according to one embodiment of thepresent invention.

FIGS. 11(a)-11(c) are schematics illustrative of another part of thehologram display fabrication method according to the first embodiment ofthe present invention.

FIGS. 12(a)-12(c) are schematics illustrative of a part of the hologramdisplay fabricating method according to another embodiment of thepresent invention.

FIGS. 13(a) and 13(b) are schematics illustrative of another part of thehologram display fabrication method according to the second embodimentof the present invention.

FIGS. 14(a)-14(c) are schematics illustrative of the hologram liquidcrystal display timepiece according to one embodiment of the presentinvention.

FIG. 15 is a schematic illustrative of how to fabricate a reflectiontype diffuse hologram.

FIG. 16 is a schematic illustrative of the directivity of a reflectiontype diffuse hologram.

FIG. 17 is a schematic illustrative of another embodiment of thehologram liquid crystal display timepiece according to the presentinvention.

FIG. 18 is a schematic illustrative of how to fabricate a transmissiontype diffuse hologram.

FIG. 19 is a schematic illustrative of the directivity of a transmissiontype diffuse hologram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the first place, the principles of the hologram replicating method,and volume hologram according to the present invention will be explainedwith some embodiments shown in the accompanying drawings.

Now consider the replication of a hologram by recording a scatteringobject in the form of a volume hologram to be used as the originalhologram plate (hereinafter often called the original plate), and thensuperposing another recording material on the original plate.

As shown in FIG. 1, illumination light 2 strikes an object O. Scatteredlight 3 coming from the object O and a portion of the illumination light2 that acts as reference light interfere in a volume hologramphotographic material 1 so that the original hologram plate can berecorded. In this case, the object O may be illuminated by, rather thanzero-order light 2 upon passing through the volume hologram photographicmaterial 1, split light separate from such light 2. Herein, let I₀ andλ₀ denote the angle of incidence, and wavelength of the reference light2 used to record the original plate, respectively.

Further, let ν₀ denote the degree of shrinkage, due to post treatmentsof the original plate, of the volume hologram photographic material 1with the original hologram recorded therein, and τ₀ denote a change inthe slant angle of (interference) fringes recorded therein. The "slantangle" is here understood to refer to an angle of the normal of thefringe surface with the normal of the surface of the volume hologramphotographic material 1.

As shown in FIG. 2, another volume hologram photographic material 4 isbrought in close contact with an original plate 1' recorded andpost-treated as shown in FIG. 1, or alternatively superposed on thatoriginal plate with a slight gap therebetween. Then, illumination light5 of wavelength λ₁ strikes a volume hologram photographic material 4 atan angle I₁ of incidence, so that the incident light 5 and diffractedlight 6 diffracted by the original plate 1' can interfere in the volumehologram photosensitive material 4 for hologram replicating purposes. Itis noted that if the original plate 1' is of the transmission type, theillumination light 5 must then be incident on the original plate 1'.

Again, let ν₁ denote the degree of shrinkage, due to post-treatments, ofthe volume hologram photographic material 4 with the hologramreplicated, and τ₁ denote a change in the slant angle of fringesrecorded therein.

Also, let n₁ and n₀ be the average refractive index, and externalrefractive index of the volume hologram photographic material 1, and 4,respectively.

Now suppose that the thus replicated volume hologram 4' is viewed from adirection lying within an angle range around an angle φ withillumination light 7 incident thereon at an angle of incidence θ, asdepicted in FIG. 3. Hereinafter, that angle of incidence θ will becalled the supposed illumination angle and that viewing angle φ will becalled the supposed viewing center angle. To enable such viewing, it isrequired that a group of fringes 8 be replicated in the volume hologram4', said group of fringes 8 being at least such that, in the vicinity ofan apex defined by the slant angle S_(g), the degree of recording isweaker farther away from the slant angle S_(g).

Before determining the condition for the angle of incidence I₁ of thereplicating illumination light 5 for the replication of such a group offringes 8, symbols used hereinafter are defined together.

I₀ is the angle of incidence of reference light for the recording of theoriginal plate.

λ₀ is the wavelength at which the original plate is recorded.

ν₀ is the degree of shrinkage of the photographic material with theoriginal hologram recorded therein.

τ₀ is the change in the slant angle of fringes recorded in the originalplate.

I₁ is the angle of incidence of the replicating illumination light.

λ₁ is the wavelength at which replication is made.

ν₁ is the degree of shrinkage of the replicating photographic material

τ₁ is the change in the slant angle in the replicated fringes.

n₀ is the external refractive index of the photographic material.

n₁ is the internal refractive index of the photographic material.

θ is the supposed illumination angle.

φ is the supposed center viewing angle.

S_(g) is the supposed slant angle.

The slant angle mentioned above should satisfy ##EQU2## wherein, forsimplicity, the angles in the photographic materials 1 and 4 are markedwith '.

When fringes having a slant angle S_(g), which are recorded in theoriginal plate 1' but not post-treated, are replicated in the replicatedand post-treated hologram 4' in the form of fringes having the sameslant angle S_(g), the pitch (inter-fringe distance) P_(t0), uponreplicated (FIG. 2), of the fringes recorded in the original plate 1' isgiven by

    P.sub.t0 =ν.sub.0 n.sub.0 λ.sub.0 /{2n.sub.1 cos (I.sub.0 '-S.sub.g -τ.sub.0)}'                                 (2)

The pitch P_(t1) (slant angle S_(g) -τ₁), upon replicated (FIG. 2), ofthe fringes recorded at the slant angle S_(g) in the replicated andpost-treated hologram 4' is given by

    P.sub.t1 =n.sub.0 λ.sub.1 /{2n.sub.1 cos (I.sub.1 '-S.sub.g +τ.sub.1)}                                            (3)

Suppose here that the refractive indices n₁ of both photographicmaterials 1 and 4 are equal, and both the fringes of the original plate1' to be replicated and the fringes to be replicated and recorded in thephotographic material 4 conform to the Bragg condition. Then,

    P.sub.t0 =P.sub.t1                                         (4)

From equations (1) to (4), we can find the angle of incidence I₁ of theillumination light 5 for replication as follows. ##EQU3##

Thus, when the original plate is replicated with the illumination light5 at the angle of incidence I₁ conforming to equation (6), a fringehaving at least a specific slant angle S_(g) is selected from amultiplicity of fringes which are formed by light 3 scattered by theobject O in multiple directions upon recording (FIG. 1) and have avariety of slant angles, so that said fringe can finally be replicatedin the form of a fringe having the same slant angle S_(g). While carehas been taken of the slant angle changes τ₀ and τ₁ in the foregoing, itis understood that they are negligible in actual volume holograms.

As can be seen from the above calculations, there are two angles ofincidence I₁ that satisfy P_(t0) =P_(t1). Variables for cosine on bothsides of equation (5), i.e., {sin⁻¹ (n₀ /n¹ ×sin I₀)-S_(g) -τ₀ } and{sin⁻¹ (n₀ /n₁ ·sin I₁)-S_(g) +τ₁ } are discriminated depending onwhether their signs are different or identical. When they have the samesign, I₁ is described as I₁ ^(A), and when they have opposite signs, I₁is described as I₁ ^(B). Consider now a pitch change at the supposedslant angle S_(g) +ΔS.

In the case of I₁ ^(A), the directions of P_(t0) and P_(t1) changes withan increase or decrease in ΔS coincide as schematically depicted in FIG.4(a). In the case of I₁ ^(B), in contrast, the directions of P_(t0) andP_(t1) changes with an increase or decrease in ΔS do not coincide asschematically depicted in FIG. 4(b). This means that the slant anglechange ΔS of a fringe with respect to a fringe meeting the Braggcondition, by which fringe incident light diffracted at the slant angleS_(g) while satisfying the Bragg condition is diffracted at half thediffraction efficiency of the first-mentioned fringe, is larger whenreplication is made at I₁ ^(A) than when replication is made at I₁ ^(B).At both I₁ ^(A) and I₁ ^(B), the diffraction efficiency of the fringe isincreased at the slant angle S_(g) equivalent to the Bragg condition. Asa certain fringe is farther away from that fringe, its diffractionefficiency becomes lower because the amount of departure from the Braggcondition becomes larger. It is thus possible to preferentially recordthe hologram of a fringe satisfying the Bragg condition and so obtain ahologram with the brightness fading out around that fringe. The degreeof this fading-out is sharper at I₁ ^(B) than at I₁ ^(A). In otherwords, a fringe having a wider slant angle S_(g) can be replicated atthe angle of incidence I₁ ^(A) than at I₁ ^(B). This means that it is atthe angle of incidence I₁ ^(A) that a hologram copy having a widervisual range (viewing angle range) around the supposed slant angle S_(g)can be obtained while it is at the angle of incidence I₁ ^(B) that ahologram copy having a narrower visual range (viewing angle range)around the supposed slant angle S_(g) can be obtained.

In one specific embodiment, if I₀ =45°, λ₀ =514.5 nm, ν₀ =0.99, λ₁=514.5 nm, n₀ =1, n₁ =1.52, θ=40°, φ=0°, and τ₀ =τ₁ =0, then S_(g)=12.51° (0.218 rad), I₁ ^(A) =40.74° (0.71 rad), and I₁ ^(B) =-0.62°(-0.01 rad). Shown in FIG. 5 are the relations between the pitch andslant angle of a fringe recorded in the original plate and the pitch andslant angle of the same fringe in the replicated and post-treatedhologram.

Thus, the present invention provides a method for replicating or copyinga volume hologram having an image of a scattering object recordedtherein by the hologram replicating technique, wherein the angle ofincidence I₁ of illumination light used for the replication of ahologram from the original hologram plate is determined from equation(6) so that a replicated hologram can be viewed at a supposed viewingcenter angle φ upon illuminated at a supposed illumination angle θ.Alternatively, the present invention provides a method for replicating avolume hologram having an image of a scattering object recorded thereinby the hologram replicating technique, wherein replicating illuminationlight is incident on the original hologram plate at an angle ofincidence I₁ that enables a fringe having a supposed slant angle S_(g)to be replicated and recorded therein so that a replicated hologram canbe viewed at a supposed viewing center angle φ upon illuminated at asupposed illumination angle θ. By use of such a hologram replicatingmethod it is possible to limit the diffraction of an unnecessary orderof light due to zero-order light, etc. arising from regular reflectionand limit a visual range capable of viewing the recorded image to adesired range, thereby replicating a hologram that can display an imagemore brightly than would be possible with the original plate.

In FIGS. 6(a) and 6(b), a conventional volume hologram having an imageof a scattering object recorded therein or a volume hologram copiedtherefrom by a conventional hologram replicating method (FIG. 6(a)) isqualitatively compared with a volume hologram replicated from a volumehologram having an image of a scattering object recorded therein by thehologram replicating method according to the present invention (FIG.6(b)). Both holograms are assumed to be reflection type volumeholograms. An image O' of a scattering object O is recorded in aconventional volume hologram or a hologram 10 copied therefrom.Therefore, when illumination light 7 strikes the volume hologram 10, theobject image O' gives out not only diffracted light 11 in a givenviewing direction but also diffracted light 12 in other scatteringdirections. In addition, diffracted light 13 corresponding to lightregularly reflected from the scattering object O upon recording is gaveout in directions other than the viewing direction. Since fringes givingout such diffracted light 12 and 13 are multi-recorded in the volumehologram 10, the index modulation of a portion of fringes giving out thediffracted light 11 contributing to real viewing is reduced and, withthis, the intensity of the diffracted light 11 becomes weak. Recorded ina volume hologram 4' replicated from a volume hologram having an imageO' of a scattering object O recorded therein according to the hologramreplicating method of the present invention, on the other hand, are onlyfringes that direct diffracted light 11 within a limited visual range α.In other words, fringes that give out diffracted light 12 in otherdirections and diffracted light 13 corresponding to light regularlyreflected from the scattering object O upon recording are removed and sonot recorded upon replication. Accordingly, the index modulation of thefringes giving out the diffracted light 11 contributing to real viewingis increased and, with this, the intensity of the diffracted light 11becomes so strong that the object image O' can be more brightly viewedthan would be possible with the original plate. Thus, the angle ofincidence I₁ of the replicating illumination light is so selected in thepresent invention that the visual range is limited upon replication.Such a limited visual range α makes it possible to increase theintensity of the diffracted light 11 therein and, hence, to view theobject image O' more brightly.

When, for instance, the hologram replicating method of the presentinvention is applied to the fabrication of a hologram diffuse plate byrecording a light diffusing plate in the form of a hologram of thescattering object O, fringes that correspond to light regularlyreflected from the light diffusing plate upon recording are removed andso not recorded upon replication. Therefore, when such a hologramdiffuse plate is built in a liquid crystal display device, etc., thedisplay device is unlikely to give out diffracted light corresponding toa regular reflection component of illumination light. It is thuspossible to obtain a hologram diffuse plate that can create brightdisplays by assigning light diffracted in a regular reflection directionto light in the direction taking part in viewing, for instance,diffracted light directing from an illumination angle of 30° toward aviewing direction of 0° (from the normal).

The volume hologram replicated by the hologram replicating method of thepresent invention is a volume hologram in which the image of thescattering object is recorded. Also recorded in this volume hologram areonly fringes that are positioned around a fringe having a slant angleS_(g) at which the volume hologram can be viewed at a given viewingcenter angle φ upon illuminated at a given illumination angle θ, andthat have a slant angle S_(g) lying within a given width ΔS with respectto the first-mentioned slant angle S_(g). Such a volume hologram can beviewed only in a direction lying within a given visual range α aroundthe viewing center angle φ; in other words, it is transparent whenviewed in other directions. According to the present invention thevisual range can be freely controlled, and so it is possible to crate avariety of images, as typically illustrated in FIG. 7. As shown, avolume hologram 20 in which, according to the present invention, thevisual range is preset in a narrow direction 23 using the aforesaidangle of incidence I₁ ^(B) of replicating illumination light as anexample, is underlaid with a pattern 21 formed by an ordinary printedpattern, etc., and the visual range 23 for the volume hologram 20 isdetermined in such a direction that the underlaid pattern 21 cannot beviewed at all. When such a superposed arrangement is illuminated byillumination light 22, only the underlaid pattern 21 can be viewed in afront direction 24 while the object recorded in the volume hologram 20can be viewed in the direction 23. Thus, the printed or otherwiseunderlaid pattern 21 and the object image recorded in the volumehologram 20 can be separately recognized.

Referring here to FIG. 8, a first fringe having a first image recordedtherein and a specific visual range α₁ and a second fringe having asecond image recorded therein and another specific visual range α₂overlapping partially with the visual range α₁ are replicated andrecorded in one single volume hologram 25 by the method of the presentinvention as will be described later. With this volume hologram 25illuminated by illumination light 22, the first hologram image can beviewed in a direction 26 within the visual region α₁, the secondhologram image can be viewed in a direction 27 within the visual regionα₂, and the first and second hologram images can be simultaneouslyviewed in a direction 28 within a region where the visual ranges α₁ andα₂ overlap. In other words, the hologram images change from one toanother by changing the viewing direction. In the practice of thepresent invention, it is understood that three or more hologram imagesmay be recorded in the volume hologram with varying visual ranges.

In order to use the method of the present invention to fabricate ahologram 25 that enables different images to be viewed for each viewingdirection, a first object image is recorded in a first volume hologramat a wavelength λ₀ and an angle of incidence I₀₁ of reference light usedfor making the original plate. In this case, the angle of incidence I₀₁of the reference light is determined from equation (6) in such a mannerthat the angle of incidence of replicating illumination light is I₁, thesupposed illumination angle is θ, and the supposed viewing center angleis φ₁ (the center angle of the visual range α₁). Then, a second objectimage is recorded in a second volume hologram at the same wavelength λ₀and an angle of incidence I₀₂ of reference light. In this case, theangle of incidence I₀₂ of the reference light is determined fromequation (6) in such a manner that the angle of incident of replicatingillumination light is I₁ as in the case of the first volume hologram,the supposed illumination angle is θ as in the case of the first volumehologram, and the supposed viewing center angle is φ₂ (the center angleof the visual region α₂). Thereafter, the first volume hologram issuperposed on the second volume hologram to form the original plate. Byreplicating that original plate using illumination light at the angle ofincidence I₁, the first and second fringes whose supposed viewing centerangles are φ₁ and φ₂ are multi-recorded in the single volume hologram25.

It is noted that the hologram 25 shown in FIG. 8 may be used as thevolume hologram 20 shown in FIG. 7. It is also noted that logotypes suchas letters, and marks may be used for one of the first and second imagesrecorded in the hologram 25 and subjects such as objects may be used forthe other.

How to fabricate a multicolor Lippmann type hologram according to themethod of the present invention will now be explained. Consider here thefabrication of a multicolor Lippmann type hologram of an objectcomprising a blue light scattering portion 31 and a red light scatteringportion 32, as shown in FIGS. 9(a)-9(c). In the first place, a bluevolume hologram photographic material 33 is located over the object 30,as shown in FIG. 9(a). Then, illumination light 34 of wavelength λ_(0B)in a blue wavelength region is incident at an angle of incidence I₀ onthe blue volume hologram photographic material 33 so that light producedby the scattering of the transmitted light at the blue light scatteringportion 31 of the object 30 and the incident light 34 interfere in theblue volume hologram photographic material 33, thereby recording a bluevolume hologram. Then, a red volume hologram photographic material 35 issuperposed on the blue volume hologram, as shown in FIG. 9(b). Then,illumination light 36 of wavelength λ_(0R) in a red wavelength region isincident at the same angle of incidence I₀ as mentioned above on the redvolume hologram photographic material 35 so that light produced by thescattering of the transmitted light at the red light scattering portion32 of the object 30 and the incident light 36 interfere in the redvolume hologram photographic material 35, thereby recording an redvolume hologram. Both materials 35 and 36, as superposed on each other,are post-treated to obtain the original plate 37.

Then, as shown in FIG. 9(c), another volume hologram photographicmaterial 38 photosensitive to both blue and red wavelength regions islocated at a position under the original plate 37, where the object 30was located for hologram recording, in such a manner that it is parallelwith the original plate 37. Whereupon, replicating illumination light39, which is composed of light of wavelength λ_(1B) in the bluewavelength region and light of wavelength λ_(1R) in the red wavelengthregion in overlapping or separate relation to each other, is incident atthe angle of incidence I₁ on the lower side of the original plate 37.Consequently, an image 30' of the object 30 is reconstructed in thevicinity of the surface of the volume hologram photographic material 38,so that the original plate 37 is replicated in the volume hologramphotographic material 38. The hologram replicated and recorded in thevolume hologram photographic material 38 in this way is a Lippmann typemulticolor image hologram (image plane hologram). Here suppose thewavelengths λ_(1B) and λ_(1R) used for replication to satisfy λ_(1B)/λ_(0B) =λ_(1R) /λ^(0R) =C (e.g., 1 if they are all the same) withrespect to the wavelengths λ_(0B) and λ_(0R) used for the recording ofthe original plate 37. It is then found from the shape of equation (6)that the same λ₁ /λ₀ =C holds whether the light is blue or red; that is,I₁ is not dependent on wavelength. Accordingly, when the same θ and φare used for both blue light and red light, holograms are recorded atthe same I₀, and replicated at the same angle of incidence I₁ of thereplicating illumination light whether the light is blue or red. In thepractice of the present invention, it is understood that it is possibleto fabricate a multicolor Lippmann type hologram in three or morecolors.

The thus fabricated multicolor Lippmann type hologram can create brightmulticolor hologram images because only fringes having the necessaryslant angle component are preferentially recorded for each color. Inaddition, the embodiment shown in FIG. 9, wherein the volume hologramphotographic material 38 is spaced away from the original plate 37during replication, enables the multicolor Lippmann type hologram to befabricated in the form of an image hologram which, even uponreconstruction in nonparallel white light, can create a clear, brighthologram image.

While the hologram replicating method, and hologram according to thepresent invention has been described with reference to the principlesand embodiments thereof, it is understood that the present invention isnot limited thereto, and so many modifications may be possible.

As can be appreciated from the foregoing explanation, the hologramreplicating method of the present invention provides a replicatedhologram which can display a hologram image more brighter than would bepossible with the original hologram plate because the diffraction of anunnecessary order of light due to zero-order light, etc., arising fromregular reflection is limited and the visual range capable of viewing arecorded image is limited to a desired range. This feature of thepresent invention is due to the fact that replicating illumination lightis incident on the original hologram plate at an angle of incidence I₁at which a group of fringes can be replicated and recorded, said groupof fringes being such that, in the vicinity of an apex defined by asupposed slant angle S_(g) at which the replicated hologram can beviewed at a supposed viewing center angle φ upon being illuminated at asupposed illumination angle θ, the recording degree of said group offringes becomes weaker at a position farther away from said slant angleS_(g).

An account will now be given of the hologram display piece according tothe present invention that is one volume hologram having an image of ascattering object recorded therein, to which the aforesaid hologramreplicating method is applied, and how to fabricate the same. Thishologram display piece is particularly suitable for cards such asidentification cards and bank cards, passbooks such as bankbooks, andforgery preventing means which verify that articles with such meansattached to them are true.

The hologram display piece of the present invention, and how tofabricate the same will now be explained with reference to somepreferred embodiments.

The hologram display piece of the present invention is basically adisplay piece that enables a specific fine pattern located behind asmall virtual opening like a keyhole to be seen through the virtualopening. Between the virtual opening and the fine pattern there is agiven distance so that the fine pattern seen through the opening canmove and change by the relative movement of the observer's visual point.Because of this action, the display piece is difficult to forge, and canbe attached to an article to pass judgment of whether it is true or not.

How to fabricate the hologram display piece of the present inventionwill now be explained with reference to one specific embodiment shown inFIGS. 10(a), 10(b), 10(c), 11(a), 11(b) and 11(c). As shown in FIG.10(a), a volume phase type hologram photographic material layer 42 suchas a photopolymer is first coated on the surface of a glass substrate41. While an opening pattern portion 43 of the hologram photographicmaterial layer 42 corresponding to a virtual opening pattern is leftintact, an area 44 of the layer 42 except the opening pattern portion 43is irradiated and deactivated with a light beam 45 such as anultraviolet beam to which the hologram photographic material layer 42 isso photosensitive that it is deactivated.

Then, as depicted in FIG. 10(b), a reflecting scatter plate is preparedby the vapor evaporation of a reflective metal such as aluminum on oneroughened surface 7 of a glass plate 46 to form a reflecting scattersurface 47. Subsequently, the surface of the reflecting scatter platethat is not opposite to the glass plate 46 is brought into close contactwith the back surface of the glass substrate 41. In this state, arecording light beam 49 is incident on the hologram photographicmaterial layer 42 at a given angle. The light beam 49 passes through theareas 43 and 44 of the hologram photographic material layer 42, goesstraightforward through the glass substrate 41 and glass plate 46, andreaches the reflecting scatter surface 47. Light 50 reflected andscattered at the surface 47 and the light beam 49 interfere in theopening pattern 43 in the hologram photographic material layer 42 toform a reflection hologram 43'.

As shown in FIG. 10(c), light 52 traveling in a direction opposite tothe traveling direction of the recording light beam 49 is incident fromthe opposite (back) side of the thus fabricated original plate 51(consisting of the glass substrate 41 and the hologram photographicmaterial layer 42 composed of the hologram-recorded area 43 and thedeactivated area 44) on the reflection hologram 43' thereof, so thatlight 53 reflected and diffracted by the reflection hologram 43' canhave action on forming an image 47' of the reflecting scatter surface 47at a position where the reflecting scatter surface 47 was originallylocated.

Then, as depicted in FIG. 11(a), another volume phase type hologramphotographic material layer 54 is coated on the back surface of theglass substrate 41 opposite to the hologram photographic material layer42 of the original plate 51, and a fine pattern portion 55 correspondingto a fine pattern is irradiated and deactivated with a light beam 57such as an ultraviolet beam to which the hologram photographic materiallayer 44 is so photosensitive that it is deactivated. At this stage, anarea 56 of the hologram photographic material layer 54 except the finepattern portion 55 is still of photosensitivity.

Subsequently, as depicted in FIG. 11(b), light 52 traveling in adirection opposite to the traveling direction of the light beam 49 usedfor the recording of the reflection hologram 43' is incident on thehologram photographic material layer 54. As explained with reference toFIG. 10(c), light 53 reflected and diffracted by the reflection hologram43' travels in such a way that an image 47' of the reflecting scattersurface 47 is formed at a position where the reflecting scatter surface47 was originally located. However, since the hologram photographicmaterial layer 54 is located on the optical axis, the light 53interferes with the incident light 52 in the photosensitive area 56except the deactivated fine pattern portion 55 to form a reflectionhologram 56'.

The hologram photographic material layer 54 with the hologram 56'recorded therein is then separated from the original plate 51. Upon theincidence on the surface side (where the original hologram photographicmaterial layer 42 was located) of light 58 traveling in a directionopposite to the traveling direction of the recording light 52, asdepicted in FIG. 11(c), the reflection hologram 56' of the hologramphotographic material layer 54 gives out diffracted light 59. This light59 is diffracted as if it was emitted from the position of the image 47'of the reflecting scatter surface 47. In addition, the diffracted light59 passes through only an area where the reflection hologram 43' waspresent at the time of such replication as shown in FIG. 11(b), so thatit can travel on the same optical path as is the case where an opening43" is present at a position of the original reflection hologram 43',resulting in the creation of a virtual opening pattern shown again at43". Any diffracted light is not emitted from the fine pattern portion55 of the hologram photographic material layer 54. Thus, when theobserver sees the hologram photographic material layer 54 in thedirection of the diffracted light 59, he can see the fine pattern 55hidden behind the small virtual opening 43" like a keyhole. Also, sincethe virtual opening 43" is spaced away from the fine pattern 55 with acertain distance d between them, the fine pattern 55 seen through theopening 43" moves and changes upon the relative movement of theobserver's visual point. It is noted that, in some cases, marginal raysother than the reconstructing light 58 are more scattered by thereflection hologram 56' than by the fine pattern portion 55. Thus, ifthere is a fear that the fine pattern may be seen even a little throughportions other than the opening 43", it is then desired that a blackabsorption layer be positioned on the side of the hologram photographicmaterial layer 54 (with the reflection hologram 56' recorded therein)that is not opposite to the virtual opening 43".

Another embodiment of the fabrication of the hologram display pieceaccording to the present invention will now be explained with referenceto FIGS. 12(i a), 12(b), 12(c), 13(a) and 13(b). As shown in FIG. 12(a),a volume phase type hologram photographic material layer 42 such as aphotopolymer is first coated on the surface of a glass substrate 41.While an opening pattern portion 43 of the hologram photographicmaterial layer 42 corresponding to the virtual opening pattern is leftintact, an area 44 of the layer 42 except the opening pattern portion 43is irradiated and deactivated with a light beam 45 such as anultraviolet beam to which the hologram photographic material layer 42 isso photosensitive that it is deactivated, as is the case with FIG.10(a).

Then, as depicted in FIG. 12(b), a reflecting scatter plate having afine pattern is prepared by coating an absorptive coating material orthe like on one roughened surface 7 of a glass plate 46 to form a fineabsorbing pattern 60, and evaporating a reflective metal 48 such asaluminum all over the roughened surface 47 through the fine pattern 60to construct a portion of the roughened surface 47 except the absorptivefine pattern 60 in the form of a reflecting scatter surface 47.Subsequently, the opposite surface of the reflecting scatter plate thatis not opposite to the glass plate 46 is brought into close contact withthe back surface of the glass substrate 41. In this state, a recordinglight beam 49 is incident on the hologram photographic material layer 42at a given angle. The light beam 49 passes through the areas 43 and 44of the hologram photographic material layer 42, goes straightforwardthrough the glass substrate 41 and glass plate 46, and reaches thereflecting scatter surface 47. Light 50 reflected and scattered at thesurface 47 and the light beam 49 interfere in the opening pattern 43 inthe hologram photographic material layer 42 to form a reflectionhologram 43'.

As shown in FIG. 12(c), light 52 traveling in a direction opposite tothe traveling direction of the recording light beam 49 is incident fromthe opposite (back) side of the thus fabricated original plate 51(consisting of the glass substrate 41 and the hologram photographicmaterial layer 42 composed of the hologram-recorded area 43 and thedeactivated area 44) on the reflection hologram 43' thereof, so thatlight 53 reflected and diffracted by the reflection hologram 43' canhave action on forming an image 47' of the reflecting scatter surface 47at a position where the reflecting scatter surface 47 was originallylocated. It is noted that the image 47' of the reflecting scattersurface 47 forms a blank area because the diffracted light 53 does notenter a pattern area 61 corresponding to the original absorptive finepattern 60.

Then, as depicted in FIG. 13(a), another volume phase type hologramphotographic material layer 62 is coated on the back surface of theglass substrate 41 opposite to the hologram photographic material layer42 of the original plate 51. For replication, light 52 traveling in adirection opposite to the traveling direction of the recording lightbeam 49 is incident on the hologram photographic material layer 62. Asexplained with reference to FIG. 12(c), light 53 reflected anddiffracted by the reflection hologram 43' travels in such a way that animage 47' of the reflecting scatter surface 47 is formed at a positionwhere the reflecting scatter surface 47 was originally located. However,since the hologram photographic material layer 62 is located on theoptical axis, the light 53 interferes with the incident light 52 to forma reflection hologram 62'.

The hologram photographic material layer 62 with the hologram 62'recorded therein is then separated from the original plate 51. Upon theincidence on the surface side (where the original hologram photographicmaterial layer 42 was located) of light 58 traveling in a directionopposite to the traveling direction of the recording light 52, asdepicted in FIG. 13(b), the reflection hologram 62' of the hologramphotographic material layer 62 gives out diffracted light 59. This light59 is diffracted as if it was emitted from the position of the image 47'of the reflecting scatter surface 47. In addition, the diffracted light59 passes through only an area where the reflection hologram 43' waspresent at the time of such replication as shown in FIG. 13(a), so thatit can travel on the same optical path as is the case where an opening43" is present at a position of the original reflection hologram 43',resulting in the creation of a virtual opening pattern shown again at43". Any diffracted light is not emitted from the pattern area 61 of theimage 47' of the reflecting scatter surface 47 corresponding to the finepattern 60. Thus, when the observer sees the hologram photographicmaterial layer 62 in the direction of the diffracted light 59, he cansee the fine pattern 61 hidden behind the small virtual opening 43" likea keyhole. Also, since the virtual opening 43" is spaced away from thefine pattern 61 with a certain distance d between them, the fine pattern61 seen through the opening 43" moves and changes upon the relativemovement of the observer's visual point. In this case, too, it isdesired that a black absorption layer be positioned on the side of thehologram photographic material layer 62 (with the hologram recordedtherein) that is not opposite to the virtual opening 43".

While the reflecting scatter surface has been described as beingobtained by the evaporation of a reflective metal such as aluminum onthe roughened surface, it is understood that use may be made of otherreflecting scatter surfaces, for instance, surfaces coated with whitecoating materials, metal plates provided with specific patterns byetching, and surfaces obtained by the repeated rounding and spreading ofaluminum foils. For photo-recording, and replication purposes (FIGS.10(b), 11(b), 12(b), and 13(a)), it is desired that the light beam (49,and 52) be incident, efficiently and without stray light, on thephotographic material layer (42, 54, and 62) that is in close contactwith a glass plate having an antireflection coating thereon. Theabsorbing fine pattern 60 shown in FIG. 12(b) may be formed on anothertransparent film, which may then be sandwiched between the glasssubstrate 41 and the glass plate 46.

A substantially similar reflection hologram 62' may be obtained bysubstituting for the reflecting scatter surface 47 having the absorbingfine pattern 60 thereon, shown in FIG. 12(b), a reflection hologram thatis obtained by irradiating and deactivating a portion of a volume phasetype hologram photographic material layer corresponding to the finepattern 60 with ultraviolet rays or the like, as shown in FIG. 10(a),and then recording the reflection hologram on a portion of thephotographic material layer other than the thus deactivated portion withlight scattered from the reflecting scatter surface 47 as shown in FIG.10(b).

It is desired that the position where the virtual opening 43" isreconstructed be a surface in the vicinity of the hologram surface,usually a surface spaced away from the hologram photographic materiallayer 54, and 62 by a distance of up to 5 cm, preferably 5 to 6 mm. Atthis surface the opening 43" is recognizable with a great aestheticeffect.

While the hologram display pieces of the present invention and how tofabricate them have been described with reference to some specificembodiments, it is understood that the present invention is not limitedthereto, and so many modifications may be possible.

As can be seen from the above explanations, the hologram display pieceof the present invention, and the method for fabricating the sameenables a fine pattern to be seen through a small virtual opening like akeyhole. Between the virtual opening and the fine pattern there is so acertain distance that the fine pattern seen through the virtual openingcan move and change upon the movement of the observer's visual point.Such action makes it possible to obtain a display piece that isdifficult to forge and can easily pass judgment on whether an articlehaving it attached thereto is true or not.

An account will now be given of embodiments of the hologram liquidcrystal display timepiece according to the present invention, whichcomprises a reflection type diffuse hologram layer that is the volumehologram having an image of a scattering body recorded therein, to whichthe aforesaid hologram replicating method is applied. This timepiece isdesigned to be improved in visibility and aesthetic effect by use of ahologram. Embodiments of the hologram liquid crystal display timepieceof the present invention will be explained.

One embodiment of the hologram liquid crystal display timepieceaccording to the present invention is shown in FIGS. 14(a), 14(b),14(c), 15 and 16. FIGS. 14(a)-14(c) show the first embodiment of thehologram liquid crystal display timepiece according to the presentinvention with (a) being a sectional schematic, (b) a schematicillustrative of a multilayer structure of a liquid crystal panel, and(c) a plan schematic. FIG. 15 is a schematic illustrative of how tofabricate a reflection type diffuse hologram, and FIG. 16 is a schematicillustrative of the directivity of a reflection type diffuse hologram.

In the hologram liquid crystal display timepiece, a reflection typediffuse hologram 73 is stacked on a back side of a liquid crystal panel71 with an index-matching liquid 72 between them, as shown in FIG.14(a). The liquid crystal panel 71 has a multilayer structure which, ascan be seen from FIG. 14(b), comprises a liquid crystal layer 71c,electrode layers 71b and 71d formed on both sides of the layer 71c, andpolarizing plates 71a and 71e located on the outside of the electrodelayers. When voltage is applied between the electrode layers, forinstance, a time display portion transmits light so that time can beindicated by light reflected and diffracted by the reflection typediffuse hologram 73, as shown in FIG. 14(c). Alternatively, a portionother than the time display portion transmits light upon voltage appliedbetween the electrode layers, so that time can be indicated. In thiscase, a logotype or other mark M, if it is recorded in the form of ahologram on the reflection type diffuse hologram, may be viewed, asshown in FIG. 14(c). Such a logotype mark may be multi-recorded directlyon the reflection type diffuse hologram 73. Alternatively, this mark maybe recorded on another plate, which may then be stacked on thereflection type diffuse hologram 73.

In the reflection type diffuse hologram 73, fringes produced by theinterference of diffusing light and reference light is recorded. To thisend, a reflection diffuse plate (scatter plate) 74 and a photographicmaterial 73 are located at a given interval, as shown in FIG. 15. Then,light 76 reflected and diffused upon the incidence of light 75 on thereflection diffuse plate 74 is directed to the back surface of thephotographic material 73 while reference light 77 strikes the frontsurface of the photographic material 73. Upon the reflection typediffuse hologram 73 irradiated with the reference light 77, it gives outreflected and diffracted light 78 corresponding to the directivity ofthe diffusing light 76 shown in FIG. 15, as can be seen from FIG. 16.Therefore, if the directivity of the diffusing light 76 is such that itis in lateral offset relation to the reference light (the direction ofthe diffusing light deviates from the direction of light produced by theregular reflection of ambient light), it is then possible to improvevisibility because the light produced by the regular reflection ofambient (reference) light does not overlap with the reflected anddiffracted light. If, in this case, the reflection type diffuse hologram73 is designed to be rotatable around the portion of the index-matchingliquid 72 shown in FIG. 14(a), it is then possible to select thedirectivity of the reflected and diffracted light. By turning thereflection type diffuse hologram 73 depending on ambient lightconditions, the timepiece can then be looked at in the absence of lightproduced by the regular reflection of ambient light. If, in this case,the turning of the hologram 73 is effected by use of the viscosity ofthe index-matching liquid 72, high visibility can be achieved withsmooth turning while the reflection of light at a liquid crystalpanel/reflecting layer interface is avoided.

Another embodiment of the hologram liquid crystal display timepieceaccording to the present invention will now be explained with referenceto FIGS. 17 to 19.

In this embodiment as shown in FIG. 17, a liquid crystal panel 81 isdisposed on the back surface of a transmission type diffuse hologram 80,and a mirror reflection plate 82 is disposed on the back surface of theliquid crystal panel 81. The liquid crystal panel 81 has a similarmultilayer structure as explained with reference to FIG. 14. Uponvoltage applied between the electrode layers, a liquid crystal portiontransmits light so that time can be indicated by light passingtherethrough and reflected from the mirror surface plate 82. Thetransmission type diffuse hologram 80 is to obtain a predetermineddirectivity, and is fabricated by allowing reference light 77 and lightcoming from a reflecting diffuse (scatter) plate 74 to interfere in thesame side of a photographic material 80 to record therein the resultantinterference fringes, as shown in FIG. 18. Upon the transmission typediffuse hologram 80 irradiated with ambient light (reference light 77)as shown in FIG. 19, it gives out transmitted and diffracted light in adirection that does not overlap with the direction of ambient light.Thus, the light incident through the transmission type diffuse hologram80 on the liquid crystal panel passes through a light-transmittingportion of the liquid crystal panel, is reflected at the mirrorreflection plate, and returns back through the light-transmittingportion of the liquid crystal panel and the transmission type diffusehologram 80, so that it can be viewed while it does not overlap withlight produced by the regular reflection of ambient light. In thisconnection, note that there is a possibility that a twin image may beformed by the rediffraction by the transmission type diffuse hologram 80of a component of the light reflected at the mirror reflection plate andreturning back through the light-transmitting portion of the liquidcrystal panel, which component is in the same direction as the referencelight or in conjugate relation thereto. However, such a twin image hasno substantial influence because the transmission type diffuse hologram80, liquid crystal panel 81 and mirror reflection plate are located inimmediate proximity to each other. In this embodiment, too, visibilityis improved by making the transmission type diffuse hologram rotatablewith respect to the liquid crystal panel so that directivity can beselected depending on ambient light conditions. It is possible to makethe field of view wide by using a diffuse plate in place of the mirrorreflection plate. It is also possible to use a reflection type diffusehologram in place of the mirror reflection plate.

According to the hologram liquid crystal display timepiece of thepresent invention as explained above, visibility can be improved becausethe reflection type diffuse hologram is disposed on the back surface ofthe liquid crystal panel or the transmission type diffuse hologram isdisposed on the front surface of the liquid crystal panel, and eachhologram has a lateral offset function so as to be free of lightproduced by the regular reflection of ambient light. A variety ofaesthetic effects can also be achieved by recording logotype marks orvarious patterns in the holograms.

What I claim is:
 1. A method for replicating an original volume hologramplate having an image of a scattering body recorded therein according toa hologram replicating technique comprising the steps of:providingreplicating illumination light incident on said original volume hologramplate at an angle of incidence I₁ at which a group of fringes can bereplicated and recorded in a replicated hologram, said group of fringesin said replicated hologram being such that, in the vicinity of an apexdefined by a slant angle S_(g) at which said replicated hologram can beviewed at a viewing center angle φ upon illumination at an illuminationangle θ, a recording degree of said group of fringes in said replicatedhologram becomes weaker more quickly at positions farther away from saidslant angle S_(g) than a recording degree of a group of fringes in saidoriginal volume hologram plate at corresponding positions away from saidslant angle relative to said original volume hologram plate,characterized in that the angle of incidence I₁ satisfies the followingequation (6): ##EQU4## where: I₀ is an angle of incidence of referencelight to record the original volume hologram plate,λ₀ is a wavelength atwhich the original volume hologram plate is recorded, ν₀ is a degree ofshrinkage of a photographic material with the original volume hologramplate recorded therein, τ₀ is a slant angle change of fringes recordedin the original volume hologram plate, λ₁ is a wavelength to replicatethe original volume hologram plate, τ₁ is a slant angle change ofreplicated fringes, n₀ is an external refractive index of thephotographic material, and n₁ is an internal refractive index of thephotographic material.
 2. A volume hologram characterized in that saidvolume hologram is fabricated by the replication method of claim
 1. 3. Avolume hologram characterized in that said volume hologram is fabricatedby the replication method of claim
 1. 4. A method for replicating anoriginal volume hologram plate with a first volume hologram having animage of a first scattering body recorded therein and a second volumehologram having an image of a second scattering body recorded therein,said holograms superposed on each other, in a single volume hologramphotographic material comprising the steps of:providing replicatingillumination light incident on the original volume hologram plate at anangle of incidence I₁ at which a first group of fringes, a second groupof fringes, and at least one additional similar group of fringes can bereplicated and recorded in a replicated hologram; said first group offringes being such that, in the vicinity of an apex defined by a firstslant angle S_(g1) at which a replicated hologram can be viewed at afirst viewing center angle φ₁ upon illumination at an illumination angleθ with respect to the hologram image of the first scattering object,wherein a recording degree of said first group of fringes becomes weakerat a position farther away from the slant angle S_(g1) than a recordingdegree of a corresponding first group of fringes in said original volumehologram; and said second group of fringes being such that, in thevicinity of an apex defined by a second slant angle S_(g2) at which thereplicated hologram can be viewed at a second viewing center angle φ₂different from the first viewing center angle φ₁ upon illumination atthe illumination angle θ with respect to the hologram image of thesecond scattering object, a recording degree of said second group offringes becomes weaker at a position farther away from said slant angleS_(g2) than a recording degree of a corresponding second group offringes in said original volume hologram, characterized in that theangle of incidence I₁ satisfies the following equation (6): ##EQU5##where: I₀ is an angle of incidence of reference light to record theoriginal volume hologram plate,λ₀ is a wavelength at which the originalvolume hologram plate is recorded, ν₀ is a degree of shrinkage of aphotographic material with the original volume hologram plate recordedtherein, τ₀ is a slant angle change of fringes recorded in the originalvolume hologram plate, λ₁ is a wavelength to replicate the originalvolume hologram plate, τ₁ is a slant angle change of replicated fringes,n₀ is an external refractive index of the photographic material, and n₁is an internal refractive index of the photographic material.
 5. Avolume hologram characterized in that said volume hologram is fabricatedby the replication method of claim
 4. 6. A method for replicating anoriginal volume hologram plate with a first volume hologram having animage of a first scattering body recorded therein at a first wavelengthand a second volume hologram having an image of a second scattering bodyrecorded therein at a second wavelength, said holograms superposed oneach other, in a single volume hologram photographic material comprisingthe steps of:providing replicating illumination light incident on theoriginal volume hologram plate at an angle of incidence I₁ such that afirst group of fringes, a second group of fringes, and at least onesimilar group of fringes can be replicated and recorded in a replicatedhologram, said first group of fringes being such that, in the vicinityof an apex defined by a first slant angle S_(g) at which said replicatedhologram can be viewed at a viewing center angle φ upon illumination atan illumination angle θ with respect to the hologram image of the firstscattering body using third illumination light having a constantwavelength ratio relation to the first wavelength, a recording degree ofsaid first group of fringes becomes weaker at a position farther awayfrom the slant angle S_(g) than a recording degree of a correspondingfirst group of fringes in said original volume hologram; and said secondgroup of fringes being such that, in the vicinity of an apex defined bythe same slant angle S_(g) at which the replicated hologram can beviewed at the same second viewing center angle φ upon illumination at anillumination angle θ with respect to the hologram image of the secondscattering object using fourth illumination light having again aconstant wavelength ratio relation to the second wavelength, a recordingdegree of said second group of fringes becomes weaker at a positionfarther away from the same slant angle S_(g) than a recording degree ofa corresponding second group of fringes in said original volumehologram, characterized in that the angle of incidence I₁ satisfies thefollowing equation (6): ##EQU6## where: I₀ is an angle of incidence ofreference light to record the original volume hologram plate,λ₀ is awavelength at which the original volume hologram plate is recorded, ν₀is a degree of shrinkage of a photographic material with the originalvolume hologram plate recorded therein, τ₀ is a slant angle change offringes recorded in the original volume hologram plate, λ₁ is awavelength to replicate the original volume hologram plate, τ₁ is aslant angle change of replicated fringes, n₀ is an external refractiveindex of the photographic material, and n₁ is an internal refractiveindex of the photographic material.
 7. A volume hologram characterizedin that said volume hologram is fabricated by the replication method ofclaim 6.